Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A typical cellular wireless system includes a number of base stations that radiate to define wireless coverage areas, such as cells and cell sectors, in which user equipment devices (UEs), such as cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices, can operate. In turn, each base station is typically coupled with equipment that provides connectivity with one or more transport networks, such as the public switched telephone network (PSTN) and/or the Internet for instance. With this arrangement, a UE operating within a coverage area of any base station can engage in air interface communication with the base station and can thereby communicate via the base station with various remote network entities or with other UEs served by the base station.
In general, a cellular wireless system may operate in accordance with a particular air interface protocol or “radio access technology,” with communications from the base stations to UEs defining a downlink (or forward link) and communications from the UEs to the base stations defining an uplink (or reverse link). Examples of existing air interface protocols include CDMA (e.g., 1xRTT and 1xEV-DO), LTE (e.g., FDD LTE and TDD LTE), WiMAX, iDEN, TDMA, AMPS, GSM, GPRS, UMTS, EDGE, MMDS, WI-FI, and BLUETOOTH. Each protocol may define its own procedures for initiation of calls, handoff between coverage areas, and functions related to air interface communication.
Further, air interface communications in each coverage area of a cellular wireless system may be encoded or carried in a manner that distinguishes the communications in that coverage area from communications in adjacent coverage areas. For example, in a CDMA system, each coverage area has a respective pseudo-random noise offset or “PN offset” that is used to encode or modulate air interface communications in the coverage area distinctly from those in adjacent coverage areas. And in an LTE system, each coverage area has a respective identifier (“cell ID” or “sector ID”) that is broadcast in a synchronization signal to distinguish the coverage area from adjacent coverage areas. Analogously, in other air interface protocols, communications in one sector may be distinguished from those in other sectors by frequency, time, and/or various other parameters.
To enable a UE to select an appropriate coverage area in which to operate, the base stations in a cellular wireless system may be arranged to broadcast in each of their coverage areas a respective pilot signal (or “reference signal”). In practice, a UE may then scan for and evaluate the strength of any detected the pilot signals, and the UE may then seek to operate in the coverage area providing the strongest pilot signal.
When a UE first powers on, the UE may go through this scanning process to select an initial coverage area in which to operate. Further, when the UE is operating in a particular coverage area, the UE may continue to monitor the pilot signal of that coverage area as well as the pilot signals of other coverage areas, to help ensure that the UE continues to operate in the coverage area providing the best coverage. In particular, if the UE detects a sufficiently strong pilot from another coverage area, the UE may then hand off from operating in its current coverage area to operating in the other coverage area.
Moreover, in some cases, more than one air interface protocol might be implemented in a given market area. For example, a given market area might provide both 3G CDMA coverage and also 4G LTE coverage. And as another example, a given market area might provide both FDD LTE coverage and TDD LTE coverage. In an area that provides two or more air interface protocols, a UE might not only hand off between coverage areas under a common air interface protocol but might also hand off between coverage areas of different air interface protocols, such as between 3G CDMA coverage and 4G LTE coverage, or between FDD LTE coverage and TDD LTE coverage.